1. Field of the Invention
The present invention relates to a method and an apparatus for peeling a protective sheet that is attached to the circuit pattern surfaces of chips after a dicing before grinding method has been conducted.
2. Description of the Related Art
As a method for producing a semiconductor wafer, a method has been known for forming a circuit pattern on the surface of a large diameter disc-shaped wafer, grinding the backside while the surface is protected by a protective tape, and peeling the protective sheet. After the semiconductor wafer is attached to a ring frame using an adhesive sheet, it is diced into a plurality of chips in cube-shape using a dicing cutter, and is transferred in this condition to the next processes of washing, drying, die bonding, etc.
With this type of method, however, there is a concern that transfer trouble and wafer breakage, etc. will occur when using an ultra-thin wafer as a result of the warping of the wafer. Recently, to deal with such issues a method called xe2x80x9cdicing before grindingxe2x80x9d has been proposed. In xe2x80x9cdicing before grindingxe2x80x9d a wafer is diced from a surface to which a circuit pattern has been formed to a prescribed depth to form bottomed grooves, and a protective sheet is attached on the wafer surface, the wafer backside is ground until reaching the bottomed grooves, and the wafer is separated into a plurality of chips. Next, after the backsides of the chips are attached to the ring frame using an adhesive sheet, the protective sheet is peeled off and the chips are transferred to the next processes of washing, drying, die bonding, etc.
Meanwhile, as a method for peeling the protective sheet from the circuit pattern surface of the wafer, a method has been known for attaching adhesive tape with a specified length to the end portion of the protective sheet and peeling the protective sheet by pulling the adhesive tape.
When performing this type of peeling, however, if the adhesive tape is pulled improperly, there is the problem of the adhesive from the protective sheet remaining on the circuit pattern. More particularly, for example, as shown in FIG. 9, on a circuit pattern 80 on a wafer W, if protective sheet is peeled in the direction of arrow A from an end portion 80A of the circuit pattern 80, the protective sheet adhesive remains on the end portion 80A.
In addition, in the case of peeling the protective sheet from the circuit pattern surface of the ultra thin chips to which a dicing before grinding method has been conducted, when attaching protective sheet to conventional chips with a thickness of approximately 350 xcexcm and modern chips with a thickness of approximately 30 xcexcm to 150 xcexcm, and then peeling the protective sheet, the rigidity of the chips will be diminished. As a result, this leads to the problem of chip breakage and damage due to the peeling resistance of the adhesive when the protective sheet is peeled.
To overcome such issues, when the inventors conducted various experiments, so that no protective sheet adhesive remains on chips C and to avoid breakage and damage to the ultra thin chips, it was verified that by regularly maintaining a specified direction in which the protective sheet is peeled it is possible to keep the adhesive from remaining on the chips and to avoid breakage and damage to the chips.
The present invention was devised in view of the above problems. An object of the present invention is to provide a method and an apparatus for peeling a protective sheet so that the adhesive of the protective sheet does not remain on the chip when the protective sheet is peeled off, and to avoid breakage and damage to ultra thin chips.
In order to achieve this object, the present invention provides a method for peeling a protective sheet that is attached to a circuit pattern surface after a dicing before grinding method is conducted on a semiconductor wafer on which a circuit pattern is formed and the semiconductor wafer is divided into chips, in which the protective sheet is peeled from the corner portions of the chips. By using this method, because the adhesion area between the protective sheet and the chips is minimized in the initial peeling period when peeling resistance is greatest, no adhesive remains on the chips and it is possible to peel the protective sheet without breakage or damage to the ultra thin chips. In other words, by peeling the protective sheet from the corner portions of the chips, the peeling resistance during the initial period can be minimized and the protective sheet can be cleanly peeled with no adhesive remaining on the corner portions of the chips, while avoiding breakage or damage to the ultra thin chips.
Also, the protective sheet peeling method can be used for chips with a thickness of 30 xcexcm to 150 xcexcm. Even with ultra thin chips, breakage and damage to the chips can be avoided for the mentioned reasons.
Furthermore, it is preferable to employ a method in which the protective sheet is peeled diagonally from the chips, and by doing so, breakage and damage to the chips can be avoided even more reliably.
Also, the present invention provides an apparatus for peeling a protective sheet that is attached to a circuit pattern surface after a dicing before grinding method is conducted on a semiconductor wafer on which the circuit pattern is formed and the wafer is divided into chips, in which a rotatable table on which the chips are placed is provided, and the rotational position of the table is controlled so that the protective sheet is peeled from the corner portions of the chips.